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    <title>Document</title>

  <title> 
     Document
  </title>
  <style>
    #top {
      background-color:aqua;
      color:tomato;
      height: 200px;
      /*垂直居中*/
      line-height: 200px;
        /*水平居中*/
      text-align: center;
    }

    #left{
      width: 200px;
      float: left;
    }

    #right{
      width: 200px;
      float: left;
    }

    audio{
      display: none;
    }

</style>
    <!--
    .top{
      background-color: aqua;
      color: blueviolet;
      height: 200px;
      /*弹性布局*/
      display: flex;
      /*垂直居中*/
      align-items: center;
      /*水平居中*/
      justify-content: center;
    }
  -->

</head>
<body>
    <div id="top">
      <h1>
      选题系统
    </h1>
    </div>
    

    <div id="middle">
      <div id="left">
        <a href="about.html" target="main">关于我们</a>
        <a href="about.html" target="main">项目情况</a>
        <a href="about.html" target="main">成员情况</a>
        <a href="about.html" target="main">学习科目介绍</a>
    </div>
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      <audio autoplay="autoplay" src="cyzy.mp3"
             controls="controls" loop="loop"
             preload="auto"></audio>
      <iframe name="main"></iframe>
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</body>
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